I'd like Trunks just due to it being so long since we last saw him and Gohan has had chances to shine in Z, but I'd be fine with either or both would be awesome, like if Trunks and Gohan started training together, and Trunks helps Gohan get back into his stride like Future Gohan did for him and even has some flashbacks or something like to the time F-Gohan told him he just had to find the right kind of motivation to get stronger.

Like cdtm said though, Vegeta stated Gohan had the most potential, and it's always kickass to see Gohan hit untold levels, so he'd definitely be interesting if he reaches that point.